1. Field of the Invention
The subject matter of the present invention is a method for increasing the resistance of igniter elements. Such alteration of resistance will be referred to hereinafter also as "trimming". Such resistance alteration is necessary especially when the igniter element is to ignite an initiating charge at a specified electrical voltage or current.
2. Discussion of Prior Art
Metal film resistances are known whose resistance is adjusted to a specified value by mechanical or optical balancing methods, wherein the conducting cross sections are adjusted to the desired value by altering the surface geometry. Such methods, however, are not suitable for the production of metal film igniting resistances, because in the igniter elements a very specific resistance must be related to a specific surface area. It is necessary, therefore, to vary the thickness of the resistance all across its area.
A known method for the practice of this alteration of the thickness of metal film igniter elements consists in an electrochemical ablation of the metal film, in which the metal film areas which are not to be removed are masked with a resist coating and thus shielded from attack by the electrical current.
This electrolytic trimming method has the disadvantage that the resist coating often is not in sufficiently intimate contact with the conducting metal and consequently unintended etching takes place on the resistances, or undercutting can take place a points where paths of conduction reach the metal films. Also, this method is not suitable for the production of metal layer igniter elements of very small size.
The problem therefore existed of developing a trimming method for metal film igniter elements which is suitable for igniter elements of very small size, and in which there is no danger that the conductor can also be attacked.